1. Field of the Invention
The present invention relates to a controller for controlling the running mode of a vehicle and, more particularly, to a curve approaching mode controller that estimates a running mode in which a vehicle will approach a curve in a road stretching ahead of the vehicle on the basis of information about the curve provided by a navigation system or the like, gives a warning to the driver and, when necessary, controls the vehicle for deceleration.
2. Description of the Related Art
There have been proposed various curve approaching mode controllers that determines an appropriate curve approaching speed for running a curve in a road stretching ahead of a vehicle on the basis of road map data stored in a navigation system and, if the actual running speed of the vehicle is higher than the appropriate curve approaching speed, gives a warning to the driver or executes a control operation to decelerate the vehicle.
A curve approaching mode controller disclosed in JP-A No. 4-236699 calculates an appropriate approach speed at which a vehicle is able to enter safely a curve in a road stretching ahead of the vehicle and having road characteristics including a radius of curvature on the basis of information about the curve in the road provided by a navigation system, gives a warning and instructs the driver to reduce the running speed of the vehicle or reduces the running speed of the vehicle automatically if the actual running speed of the vehicle is higher than the appropriate approach speed.
This prior art curve approaching mode controller is able to control the curve approaching mode of the vehicle only when the information about the curve in the road stretching ahead of the vehicle is available from the navigation system. Therefore, the curve approaching mode controller stops warning the driver and controlling the vehicle for deceleration when the information about the curve in the road is unavailable from the navigation system. For example, when a road is under construction and the vehicle is compelled to take a detour or when the vehicle short-cuts a road, the navigation system is unable to find the position of the vehicle in the road map data stored therein, is unable to provide data on the road stretching ahead of the vehicle and, consequently, there is the possibility that the curve approaching mode controller stops control operations for warning the driver and decelerating the vehicle. It is possible that the position of a vehicle goes out of road map data stored in the navigation system while the vehicle is running in the vicinity of a curve in a road or a crossing due to errors in the road map data or errors in the absolute position of the vehicle indicated by the GPS (global positioning system). In such a case, the navigation system is unable to provide road data on the road stretching ahead of the vehicle and, consequently, the curve approaching mode controller stops control operations for warning the driver and decelerating the vehicle.
The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide a curve approaching mode controller capable of continuing control operations for controlling the running of a vehicle to some extent even if any information about a curve in a road stretching ahead of a vehicle is unavailable from the navigation system, capable of instructing the driver of a vehicle according to natural conditions and capable of being easily used.
According to the present invention, a curve approaching mode controller includes: a curve information retrieving unit for retrieving curve information about a curve in a road stretching ahead of a vehicle; and a control unit for estimating a curve approaching mode in which the vehicle will approach the curve on the basis of the curve information retrieved by the curve information retrieving unit and executing predetermined control operations; wherein the control unit estimates, when the curve information retrieved by the curve information retrieving unit is insufficient for curve approaching mode estimation, a curve approaching mode in which the vehicle will approaches the curve on the basis of curve information provided before the curve information becomes insufficient.
Preferably, the control unit completes a curve approaching mode estimating operation in a predetermined time period when the curve information is insufficient. Also, it is preferred that the control unit completes a curve approaching mode estimating operation while the vehicle travels a predetermined distance when the curve information is insufficient.
According to the present invention, the curve information retrieving unit retrieves the curve information about a curve in a road stretching ahead of the vehicle, and the control unit estimates a curve approaching mode in which the vehicle will approach the curve on the basis of the curve information and executes control operations. If the estimation of a curve approaching mode in which the vehicle will approach the curve is difficult because the curve information retrieved by the curve information retrieving unit is insufficient, the control unit estimates a curve approaching mode on the basis of curve information provided before the curve information becomes insufficient. Therefore, a vehicle control operation is continued for the longest possible time even if curve information is not available from the curve information retrieving unit. Thus, the curve approaching mode controller is able to instruct the driver of a vehicle according to natural conditions and is easy to use.
According to the present invention, the control unit estimates the curve approaching mode in a predetermined time period or while the vehicle travels a predetermined distance when the curve information provided by the curve information retrieving unit is insufficient. Therefore, the execution of an improper control operation can be surely prevented while the vehicle is traveling a road where curve information is unavailable and the increase of errors in the accuracy of control can be avoided.